1. Field of the Invention
This invention relates generally to a hearing aid and, more particularly, to a hearing aid incorporating a novelty filter providing adaptable gain in a plurality of channels.
2. Discussion of the Related Art
Conventional hearing aids come in a variety of shapes and styles. Typically, however, every hearing aid will consist of a microphone, an amplifier, and an ear phone, sometimes known as a driver. The microphone will be directed towards the environment and the ear phone will be directed towards a user's ear drum such that environmental sounds sensed by the microphone will be amplified by the amplifier and delivered to the ear phone to enable the user to perceive these sounds. More sophisticated hearing aid models may incorporate several channels of amplification, each channel being assigned a particular frequency band by a bandpass filter within the normal hearing range. Whatever designs and features a hearing aid incorporates, a number of problems must be addressed in design. Typical problems encountered by a hearing aid user include feedback between the microphone and the ear phone, inappropriate gain settings of the amplifier in one or more of the channels, and poor battery life.
Feedback occurs due to the fact that the hearing aid is a high gain (30 dB or more) device in which the microphone and the ear phone are generally spaced less than one inch apart from each other within a common housing. When a hearing aid is fitted to a particular user, usually the seal between the hearing aid housing and the user's ear canal ensures acoustic isolation between the microphone and the earphone, thus substantially eliminating feedback. However, through normal use of the aid and age of the user, certain factors, such as the shape of the ear canal, cause loss of isolation between the microphone and the earphone, thus producing feedback. Consequently, the hearing aid may have to be replaced or readjusted.
Many conventional hearing aids use a number of channels of amplification having a fixed gain setting for each channel. Typically, the gain is preset by the hearing aid dealer or audiologist. Environmental acoustics or high levels of noise may all conspire to make gain settings which are ideal at the hearing aid dealer's office inappropriate for the particular idiosyncracies of the user's environment. Consequently, since the gain is preset, a hearing aid user will not realize the most desirable gain for each channel of the hearing aid in the environments the user may encounter. Additionally, each amplification channel amplifies not only the desirable sounds, but those of unwanted background noise as well. Certain hearing aids may, however, incorporate automatic gain control (AGC) or output limiting in which the hearing aid automatically limits the intensity of the amplification of a sound.
What is needed then is a hearing aid which compensates for feedback, and which provides an adaptively adjustable gain in each channel in order to selectively amplify desirable sounds. It is therefore an object of the present invention to provide such a hearing aid.